scholarly journals Deficit of Mitonuclear Genes on the Human X Chromosome Predates Sex Chromosome Formation

2015 ◽  
Vol 7 (2) ◽  
pp. 636-641 ◽  
Author(s):  
Rebecca Dean ◽  
Fabian Zimmer ◽  
Judith E. Mank
Keyword(s):  
X Chromosome ◽  
Sex Chromosome ◽  
Chromosome Formation

scholarly journals Complex evolutionary history of the Y chromosome in flies of the Drosophila obscura species group

2019 ◽  
Author(s):  
Ryan Bracewell ◽  
Doris Bachtrog
Keyword(s):  
X Chromosome ◽  
Sex Chromosomes ◽  
Evolutionary History ◽  
Sex Chromosome ◽  
Species Group ◽  
Genomic Environment ◽  
History Of ◽  
Chromosome Formation ◽  
Dramatic Variation ◽  
Complex Evolutionary History

The Drosophila obscura species group shows dramatic variation in karyotype, including transitions among sex chromosomes. Members of the affinis and pseudoobscura subgroups contain a neo-X chromosome (a fusion of the X with an autosome), and it was shown that ancestral Y genes of Drosophila have become autosomal in species that contain the neo-X. Detailed analysis in species of the pseudoobscura subgroup revealed a translocation of ancestral Y genes to the small dot chromosome of that group. Here, we show that the Y-dot translocation is restricted to the pseudoobscura subgroup, and translocation of Y genes in the affinis subgroup followed a different route. We find that most ancestral Y genes moved independently to autosomal or X-linked locations in different taxa of the affinis subgroup, and we propose a dynamic model of sex chromosome formation and turnover in the obscura species group. Our results show that Y genes can find unique paths to escape an unfavorable genomic environment.

scholarly journals Complex Evolutionary History of the Y Chromosome in Flies of the Drosophila obscura Species Group

2020 ◽  
Vol 12 (5) ◽  
pp. 494-505
Author(s):  
Ryan Bracewell ◽  
Doris Bachtrog
Keyword(s):  
Detailed Analysis ◽  
X Chromosome ◽  
Sex Chromosomes ◽  
Evolutionary History ◽  
Sex Chromosome ◽  
Species Group ◽  
History Of ◽  
Chromosome Formation ◽  
Dramatic Variation ◽  
Complex Evolutionary History

Abstract The Drosophila obscura species group shows dramatic variation in karyotype, including transitions among sex chromosomes. Members of the affinis and pseudoobscura subgroups contain a neo-X chromosome (a fusion of the X with an autosome), and ancestral Y genes have become autosomal in species harboring the neo-X. Detailed analysis of species in the pseudoobscura subgroup revealed that ancestral Y genes became autosomal through a translocation to the small dot chromosome. Here, we show that the Y-dot translocation is restricted to the pseudoobscura subgroup, and translocation of ancestral Y genes in the affinis subgroup likely followed a different route. We find that most ancestral Y genes have translocated to unique autosomal or X-linked locations in different taxa of the affinis subgroup, and we propose a dynamic model of sex chromosome formation and turnover in the obscura species group. Our results suggest that Y genes can find unique paths to escape unfavorable genomic environments that form after sex chromosome–autosome fusions.

scholarly journals Bisection of the X chromosome disrupts the initiation of chromosome silencing during meiosis in Caenorhabditis elegans

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yisrael Rappaport ◽  
Hanna Achache ◽  
Roni Falk ◽  
Omer Murik ◽  
Oren Ram ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Rna Polymerase Ii ◽  
X Chromosome ◽  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Transcription Analysis ◽  
X Chromosomes ◽  
Unique Character ◽  
Active Transcription ◽  
Heterogametic Sex

AbstractDuring meiosis, gene expression is silenced in aberrantly unsynapsed chromatin and in heterogametic sex chromosomes. Initiation of sex chromosome silencing is disrupted in meiocytes with sex chromosome-autosome translocations. To determine whether this is due to aberrant synapsis or loss of continuity of sex chromosomes, we engineered Caenorhabditis elegans nematodes with non-translocated, bisected X chromosomes. In early meiocytes of mutant males and hermaphrodites, X segments are enriched with euchromatin assembly markers and active RNA polymerase II staining, indicating active transcription. Analysis of RNA-seq data showed that genes from the X chromosome are upregulated in gonads of mutant worms. Contrary to previous models, which predicted that any unsynapsed chromatin is silenced during meiosis, our data indicate that unsynapsed X segments are transcribed. Therefore, our results suggest that sex chromosome chromatin has a unique character that facilitates its meiotic expression when its continuity is lost, regardless of whether or not it is synapsed.

scholarly journals Absence of X-chromosome dosage compensation in the primordial germ cells of Drosophila embryos

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ryoma Ota ◽  
Makoto Hayashi ◽  
Shumpei Morita ◽  
Hiroki Miura ◽  
Satoru Kobayashi
Keyword(s):  
X Chromosome ◽  
Germ Cells ◽  
Dosage Compensation ◽  
Sex Chromosome ◽  
Primordial Germ Cells ◽  
Histone H4 ◽  
X Chromosomes ◽  
Essential Components ◽  
Msl Complex ◽  
Male Specific

AbstractDosage compensation is a mechanism that equalizes sex chromosome gene expression between the sexes. In Drosophila, individuals with two X chromosomes (XX) become female, whereas males have one X chromosome (XY). In males, dosage compensation of the X chromosome in the soma is achieved by five proteins and two non-coding RNAs, which assemble into the male-specific lethal (MSL) complex to upregulate X-linked genes twofold. By contrast, it remains unclear whether dosage compensation occurs in the germline. To address this issue, we performed transcriptome analysis of male and female primordial germ cells (PGCs). We found that the expression levels of X-linked genes were approximately twofold higher in female PGCs than in male PGCs. Acetylation of lysine residue 16 on histone H4 (H4K16ac), which is catalyzed by the MSL complex, was undetectable in these cells. In male PGCs, hyperactivation of X-linked genes and H4K16ac were induced by overexpression of the essential components of the MSL complex, which were expressed at very low levels in PGCs. Together, these findings indicate that failure of MSL complex formation results in the absence of X-chromosome dosage compensation in male PGCs.

scholarly journals X-Linked Signature of Reproductive Isolation in Humans is Mirrored in a Howler Monkey Hybrid Zone

2020 ◽  
Vol 111 (5) ◽  
pp. 419-428 ◽  
Author(s):  
Marcella D Baiz ◽  
Priscilla K Tucker ◽  
Jacob L Mueller ◽  
Liliana Cortés-Ortiz
Keyword(s):  
Reproductive Isolation ◽  
X Chromosome ◽  
Hybrid Zone ◽  
Sex Chromosome ◽  
Genomic Sequence ◽  
Alouatta Palliata ◽  
Model Systems ◽  
Howler Monkey ◽  
Autosomal Snps ◽  
Outlier Region

Abstract Reproductive isolation is a fundamental step in speciation. While sex chromosomes have been linked to reproductive isolation in many model systems, including hominids, genetic studies of the contribution of sex chromosome loci to speciation for natural populations are relatively sparse. Natural hybrid zones can help identify genomic regions contributing to reproductive isolation, like hybrid incompatibility loci, since these regions exhibit reduced introgression between parental species. Here, we use a primate hybrid zone (Alouatta palliata × Alouatta pigra) to test for reduced introgression of X-linked SNPs compared to autosomal SNPs. To identify X-linked sequence in A. palliata, we used a sex-biased mapping approach with whole-genome re-sequencing data. We then used genomic cline analysis with reduced-representation sequence data for parental A. palliata and A. pigra individuals and hybrids (n = 88) to identify regions with non-neutral introgression. We identified ~26 Mb of non-repetitive, putatively X-linked genomic sequence in A. palliata, most of which mapped collinearly to the marmoset and human X chromosomes. We found that X-linked SNPs had reduced introgression and an excess of ancestry from A. palliata as compared to autosomal SNPs. One outlier region with reduced introgression overlaps a previously described “desert” of archaic hominin ancestry on the human X chromosome. These results are consistent with a large role for the X chromosome in speciation across animal taxa and further, suggest shared features in the genomic basis of the evolution of reproductive isolation in primates.

Sperm Competition and the Dynamics of X Chromosome Drive: Stability and Extinction

Genetics ◽  
2002 ◽  
Vol 160 (4) ◽  
pp. 1721-1731 ◽  
Author(s):  
Jesse E Taylor ◽  
John Jaenike
Keyword(s):  
Sex Ratio ◽  
Sperm Competition ◽  
X Chromosome ◽  
Sex Chromosome ◽  
Basin Of Attraction ◽  
Male Mating ◽  
Male And Female ◽  
Mating Rate ◽  
Female Mating ◽  
Balanced Polymorphism

AbstractSeveral empirical studies of sperm competition in populations polymorphic for a driving X chromosome have revealed that Sex-ratio males (those carrying a driving X) are at a disadvantage relative to Standard males. Because the frequency of the driving X chromosome determines the population-level sex ratio and thus alters male and female mating rates, the evolutionary consequences of sperm competition for sex chromosome meiotic drive are subtle. As the SR allele increases in frequency, the ratio of females to males also increases, causing an increase in the male mating rate and a decrease in the female mating rate. While the former change may exacerbate the disadvantage of Sex-ratio males during sperm competition, the latter change decreases the incidence of sperm competition within the population. We analyze a model of the effects of sperm competition on a driving X chromosome and show that these opposing trends in male and female mating rates can result in two coexisting locally stable equilibria, one corresponding to a balanced polymorphism of the SR and ST alleles and the second to fixation of the ST allele. Stochastic fluctuations of either the population sex ratio or the SR frequency can then drive the population away from the balanced polymorphism and into the basin of attraction for the second equilibrium, resulting in fixation of the SR allele and extinction of the population.

scholarly journals Parallel Universes for Models of X Chromosome Dosage Compensation in Drosophila: A Review

2016 ◽  
Vol 148 (1) ◽  
pp. 52-67 ◽  
Author(s):  
James A. Birchler
Keyword(s):  
X Chromosome ◽  
Dosage Compensation ◽  
Sex Chromosome ◽  
Fold Increase ◽  
Molecular Data ◽  
X Chromosomes ◽  
Histone Modifiers ◽  
Parallel Universes ◽  
Msl Complex ◽  
High Level

Dosage compensation in Drosophila involves an approximately 2-fold increase in expression of the single X chromosome in males compared to the per gene expression in females with 2 X chromosomes. Two models have been considered for an explanation. One proposes that the male-specific lethal (MSL) complex that is associated with the male X chromosome brings histone modifiers to the sex chromosome to increase its expression. The other proposes that the inverse effect which results from genomic imbalance would tend to upregulate the genome approximately 2-fold, but the MSL complex sequesters histone modifiers from the autosomes to the X to mute this autosomal male-biased expression. On the X, the MSL complex must override the high level of resulting histone modifications to prevent overcompensation of the X chromosome. Each model is evaluated in terms of fitting classical genetic and recent molecular data. Potential paths toward resolving the models are suggested.

Abstract WP325: X, but Not Y, Sex Chromosome Contributes to Stroke Sensitivity in Aged Mice

Stroke ◽  
2020 ◽  
Vol 51 (Suppl_1) ◽  
Author(s):  
Shaohua Qi ◽  
Abdullah Al Mamun ◽  
Romana Sharmeen ◽  
Conelius Ngwa ◽  
Louise D. McCullough ◽  
...  
Keyword(s):  
X Chromosome ◽  
Sex Chromosome ◽  
Elderly Women ◽  
The Elderly ◽  
Artery Occlusion ◽  
Natural Menopause ◽  
Aged Mice ◽  
Tnf Α ◽  
Significant Difference ◽  
Four Core Genotype

Introduction: Stroke is a sexually dimorphic disease. Women are protected against ischemia compared to men before menopause due to estrogen’s neuroprotection; after menopause the elderly women become vulnerable to stroke attack. Our previous studies with four core genotype mice found a chromosomal effect (either X or Y) in stroke sensitivity. Recently, we found two X-linked genes ( Kdm6a and Kdm5c ) that escape from X chromosome inactivation (XCI) are higher expressed in aged female vs. male microglia after stroke. KDM6A and KDM5C are histone demethylases that modify gene expression of inflammatory mediators. By these early studies, we hypothesized that the second X chromosome contributes to stroke sensitivity in aged mice through immune responses mediated by KDM6A and KDM5C. Methods: XY* aged (18-22 months) mice (natural menopause cohort) that have four genotypes (XO, XX, XY, XXY) were subjected to middle cerebral artery occlusion (MCAO). Another cohort of gonadectomized XY* mice were also used as the “surgical menopause” cohort. Infarct volumes and behavior deficits were quantified 3 days after MCAO. KDM6A and KDM5C localization with microglial marker TMEM119 was examined by IHC. Plasma inflammatory cytokine (IL-1β, TNF-α, IL-6, IL-4, TL-10, etc.) levels were analyzed with MultiPlex. The contribution of the second X-chromosome to stroke sensitivity was determined by comparing XX vs. XO or XXY vs. XY mice, and the effect of the Y-chromosome was evaluated by a comparison between XY vs. XO and XXY vs. XX mice. Results: In both surgical and natural menopause cohorts, XX and XXY mice showed worse stroke outcomes compared to XO or XY mice respectively; however, no significant difference was found between XX vs. XXY or XO vs. XY mice. IHC results showed higher expression of KDM6A and KDM5C in TMEM119 positive cells in mice with two vs. one copy of X chromosome. XXY mice had significantly higher levels of circulating TNF-α and IL-6 than XY mice. Conclusion: The second X chromosome contributes to stroke sensitivity in mice. Kdm6a and Kdm5c may play important roles in mediating post-stroke inflammation. Future work will genetically manipulate the expression of Kdm6a and Kdm5c in microglia to examine the roles of the two XCI escapee gene in stroke.

scholarly journals A second X chromosome contributes to resilience in a mouse model of Alzheimer’s disease

2020 ◽  
Vol 12 (558) ◽  
pp. eaaz5677 ◽  
Author(s):  
Emily J. Davis ◽  
Lauren Broestl ◽  
Samira Abdulai-Saiku ◽  
Kurtresha Worden ◽  
Luke W. Bonham ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Y Chromosome ◽  
X Chromosome ◽  
Sex Chromosome ◽  
Testicular Development ◽  
X Chromosomes ◽  
Model Of Alzheimer’S Disease ◽  
Preclinical Ad ◽  
Brain Expression

A major sex difference in Alzheimer’s disease (AD) is that men with the disease die earlier than do women. In aging and preclinical AD, men also show more cognitive deficits. Here, we show that the X chromosome affects AD-related vulnerability in mice expressing the human amyloid precursor protein (hAPP), a model of AD. XY-hAPP mice genetically modified to develop testicles or ovaries showed worse mortality and deficits than did XX-hAPP mice with either gonad, indicating a sex chromosome effect. To dissect whether the absence of a second X chromosome or the presence of a Y chromosome conferred a disadvantage on male mice, we varied sex chromosome dosage. With or without a Y chromosome, hAPP mice with one X chromosome showed worse mortality and deficits than did those with two X chromosomes. Thus, adding a second X chromosome conferred resilience to XY males and XO females. In addition, the Y chromosome, its sex-determining region Y gene (Sry), or testicular development modified mortality in hAPP mice with one X chromosome such that XY males with testicles survived longer than did XY or XO females with ovaries. Furthermore, a second X chromosome conferred resilience potentially through the candidate gene Kdm6a, which does not undergo X-linked inactivation. In humans, genetic variation in KDM6A was linked to higher brain expression and associated with less cognitive decline in aging and preclinical AD, suggesting its relevance to human brain health. Our study suggests a potential role for sex chromosomes in modulating disease vulnerability related to AD.

scholarly journals The sex chromosome association (Sxa) gene is located on the X-chromosome in mice.

1990 ◽  
Vol 65 (2) ◽  
pp. 65-69 ◽  
Author(s):  
Hirotami T. IMAI ◽  
Masayasu Y. WADA ◽  
Kazuo MORIWAKI
Keyword(s):  
X Chromosome ◽  
Sex Chromosome ◽  
Chromosome Association
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